1. Field of the Invention
The present invention relates to an image pickup apparatus such as a digital camera and a control method therefor, which are capable of changing an operation condition of an image sensing device according to image shooting condition.
2. Description of the Related Art
Some image pickup apparatus is configured to operate an image sensing device such as a CMOS sensor in an operation condition that varies according to image shooting condition. For example, there is an image pickup apparatus that increases gains of pixel amplifiers of an image sensing device with increase of image shooting sensitivity. To this end, floating diffusion units (hereinafter each referred to as FD) that accumulate electrical charges generated in pixels are each configured to have a small capacity. However, with decrease of the FD capacity, an amount of charge that can be transferred decreases and as result a so-called dynamic range becomes narrow.
To obviate this, there is known an image pickup apparatus that changes the FD capacity by using e.g. a MOS transistor connected to the FD to thereby change the amount of charge that can be held in the FD, thereby expanding the dynamic range (see, Japanese Laid-open Patent Publication No. 2000-165754).
It should be noted that with increase of the FD capacity, not only the dynamic range increases, but also noise increases. On the other hand, the dynamic range becomes narrow with decrease of the FD capacity, as previously described.
According to the image pickup apparatus disclosed in Japanese Laid-open Patent Publication No. 2000-165754, the dynamic range can be expanded, however, it is difficult to reduce noise and expand the dynamic range at the same time. In a case, for example, that pieces of pixel data in the same column are added together, it is difficult to simultaneously achieve dynamic range expansion and noise reduction.